- [Instructor] We now want to look at troubleshooting SNMP,
both version 2c and version 3.
Before we look at the specific steps for each version,
let's talk about some general troubleshooting steps.
Regardless of the version, you want to start
with where we start with most things,
and that's making sure that you have layer 3 connectivity
through a simple ping test.
Make sure you can ping the SNMP server
from the agent device.
You'll also want to make sure UDP ports 161 and 162
are not being blocked.
SNMP uses UDP port 161 for general messages
and UDP port 162 for trap messages.
Now let's discuss some specific steps
for SNMP version 2c troubleshooting.
We can take a look at my configuration
by saying show run, and I'll say pipe to section SNMP.
The specific things that you'll want to check for first
are that your community strings match.
You can see that my community string is ENARSI in all caps,
and so the Cisco router in my case
is configured as an SNMP agent.
So in order for the SNMP management server
to read or write from the agent,
the community strings must match on both sides,
both here and on the server itself.
Also at the end, notice we see the number 50,
this means ACL 50 is being used to define which IP addresses
are able to read from the agent.
So if I say show IP access-lists,
and I call out access list 50,
you can see that I have a single permit statement in here
for the IP address 10.1.1.50,
which is my SNMP management server.
If you have an ACL indicated as I do here in my output,
then you'll want to check
for that specific access control list
and you'll want to look through the entries on there
to make sure that you've permitted
the correct IP address inside the ACL.
And you'll want to make sure that it matches
your management server's IP address.
Going back to the SNMP configuration output,
we see the enable traps command here, this line,
and we see also specifically that I've only selected
OSPF version 3 errors.
But if you leave this last part off,
if you leave OSPF version 3 errors off,
if you have only this section,
if you have SNMP-server enable traps,
that means that it's going to allow all of the messages,
it's going to send everything
instead of something very specific.
So that's another place you would want to double check.
We see a line indicating the server's IP address.
The host at 10.1.1.50.
So again, you want to make sure that the correct IP address
is in place here as well,
and that this matches any ACL attached to the configuration.
We also see the informs keyword.
That's another important place to check.
So we can set this as either a trap or an inform.
Informs require a confirmation of message receipt
from the management server,
while traps, they simply send messages
without requiring any confirmation.
So obviously, traps are less reliable,
because you don't receive an acknowledgement
from the server.
Now the tradeoff is that traps consume less resources,
both on the device and in the network.
So that's a determination you need to make on your own.
Within this line, we also see the SNMP version,
in this case, that's version 2c.
So this command tells us
that we are sending SNMP version 2c in four messages
to our server at 10.1.1.50,
and again, another thing to note here
is with this particular command,
we're only sending those OSPF version 3 errors.
It's possible that you're sending all traps.
And at the very end, we again see our community string,
ENARSI in all caps.
Another place you want to make sure
that that is correctly specified.
So again, just to reiterate,
you want to check your community string.
You want to check your ACL for anything
that might be blocked,
and you want to make sure that you have enabled
the correct traps.
If you're not seeing what you're looking for,
those may actually be filtered out.
Now by default, all of the messages are going to be sent.
So unless you've specified something specific,
you should be getting messages from everything.
So that's a look at SNMP version 2c troubleshooting.
In our next video, we'll look at troubleshooting
an SNMP version 3 configuration.